Trim, Control, and Performance Effects in Variable-Complexity High-Speed Civil Transport Design

Numerous trim, control requirements and mission generalizations have been made to our previous multidisciplinary design methodology for a high speed civil transport. We optimize the design for minimum take off gross weight, including both aerodynamics and structures to find the wing planform and thickness distribution, fuselage shape, engine placement and thrust, using 29 design variables. While adding trim and control it was found necessary to simultaneously consider landing gear integration. We include the engine-out and crosswind landing requirements, as well as engine nacelle ground strike for lateral-directional requirements. For longitudinal requirements we include nose-wheel lift-off rotation and approach trim as the critical conditions. We found that the engine-out condition and the engine nacelle ground strike avoidance were critical conditions. The addition of a horizontal tail to provide take-off rotation resulted in a signiffcant weight penalty, and that penalty proved to be sensitive to the position of the landing gear. We include engine sizing with thrust during cruise and balanced field length conditions. Both the thrust during cruise and balanced field length constraints were critical. We include a subsonic leg in our mission analysis. The addition of a subsonic mission requirement also results in a large weight penalty.